Method and apparatus for forming a coating

ABSTRACT

A method for forming a coating on a substrate using an atmospheric pressure plasma discharge. The method comprises introducing an atomized liquid and/or solid coating-forming material into an atmospheric pressure plasma discharge and/or an ionized gas stream resulting therefrom, and exposing the substrate to the atomized coating-forming material. The application also described a method for polymerizing a polymer forming material, and further to apparatus for forming a coating on a substrate.

FIELD OF INVENTION

[0001] The present invention relates to a method for forming a coatingon a substrate, in particular a method for forming a coating on asubstrate using an atmospheric pressure plasma discharge, a method forpolymerizing a polymer forming material, and further to apparatus forforming a coating on a substrate.

BACKGROUND OF THE INVENTION

[0002] Substrates may be coated for a variety of reasons, for example toprotect the substrate from corrosion, to provide a barrier to oxidation,to improve adhesion with other materials, to increase surface activity,and for reasons of biomedical compatibility of the substrate. A commonlyused method for modifying or coating the surface of a substrate is toplace the substrate within a reactor vessel and subject it to a plasmadischarge. Many examples of such treatment are known in the art; forexample, U.S. Pat. No. 5,876,753 discloses a process for attachingtarget materials to a solid surface which process includes affixingcarbonaceous compounds to a surface by low power variable duty cyclepulsed plasma deposition, and EP-A-0896035 discloses a device having asubstrate and a coating, wherein the coating is applied to the substrateby plasma polymerization of a gas comprising at least one organiccompound or monomer. DE 19924108, which was first published after theinitial priority date of the present application, describes a processfor coating dyestuffs and corrosion inhibitors onto substrates. Theprocess involves the application of a liquid film coating onto asubstrate and a subsequent plasma polymer protective coating. The plasmapolymer coating is formed using gaseous monomers and low pressureplasma.

[0003] However, such plasma surface treatments require the substrate tobe under conditions of reduced pressure, and hence require a vacuumchamber. Typical coating-forming gas pressures are in the range 5 to 25Nm⁻² (cf. 1 atmosphere=1.01×10⁵ Nm⁻²). As a result of the requirementfor reduced pressure, surface treatments are expensive, are limited tobatch treatments, and the coating-forming materials must be in gaseousand/or vapor form in order to maintain conditions of reduced pressure.

[0004] The present inventors have found that the abovementioneddisadvantages of substrate surface plasma treatment can be overcomeusing a combination of an atmospheric pressure plasma discharge and anatomized liquid and/or solid coating forming material.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005]FIG. 1 is a schematic drawing of an apparatus useful in thisinvention.

DETAILED DESCRIPTION OF TH INVENTION

[0006] Thus, according to the present invention there is provided amethod for forming a coating on a substrate, which method comprisesintroducing an atomized liquid and/or solid coating-forming materialinto an atmospheric pressure plasma discharge and/or an ionized gasstream resulting therefrom, and exposing the substrate to the atomizedcoating-forming material under conditions of atmospheric pressure.

[0007] It is to be understood that the coating forming material inaccordance with the present invention is a material that can be used tomake any appropriate coating, including, for example, a material thatcan be used to grow a film or to chemically modify an existing surface.

[0008] The present invention also provides a method for polymerizing apolymer-forming material, which method comprises atomizing thepolymer-forming material, and exposing the polymer-forming material toan atmospheric pressure plasma discharge.

[0009] The present invention further provides apparatus for forming acoating on a substrate, which apparatus comprises means for generatingan atmospheric pressure plasma discharge within which, in use, thesubstrate is placed, an atomizer for providing an atomizedcoating-forming material within the plasma discharge, and means forsupplying a coating forming material to the atomizer.

[0010] Any conventional means for generating an atmospheric pressureplasma glow discharge may be used in the present invention, for exampleatmospheric pressure plasma jet, atmospheric pressure microwave glowdischarge and atmospheric pressure glow discharge. Typically such meanswill employ a helium diluents and a high frequency (e.g.>1 kHz) powersupply to generate a homogeneous glow discharge at atmospheric pressurevia a Penning ionization mechanism, (see for example, Kanazawa et al, J.Phys. D: Appl. Phys. 1988, 21, 838, Okazaki et al, Proc. Jpn. Symp.Plasma Chem. 1989, 2, 95, Kanazawa et al, Nuclear Instruments andMethods in Physical Research 1989, B37/38, 842, and Yokoyama et al., J.Phys. D: Appl. Phys. 1990, 23, 374).

[0011] The coating-forming material may be atomized using anyconventional means, for example an ultrasonic nozzle. The atomizerpreferably produces a coating-forming material drop size of from 10 to100 μm, more preferably from 10 to 50 μm. Suitable atomizers for use inthe present invention are ultrasonic nozzles from Sono-Tek Corporation,Milton, N.Y., USA. The apparatus of the present invention may include aplurality of atomizers, which may be of particular utility, for example,where the apparatus is to be used to form a copolymer coating on asubstrate from two different coating-forming materials, where themonomers are immiscible or are in different phases, e.g. the first is asolid and the second is gaseous or liquid.

[0012] The present invention may be used to form many different types ofsubstrate coatings. The type of coating which is formed on the substrateis determined by the coating-forming material(s) used, and the presentmethod may be used to (co)polymerize coating-forming monomer material(s)onto the substrate surface. The coating-forming material may be organicor inorganic, solid, liquid or gaseous, or mixtures thereof. Suitableorganic coating-forming materials may be selected from the group ofcarboxylates, methacrylates, acrylates, styrenes, methacrylonitriles,alkenes and dienes, for example methyl methacrylate, ethyl methacrylate,propyl methacrylate, butyl methacrylate, and other alkyl methacrylates,and the corresponding acrylates, including organofunctionalmethacrylates and acrylates, including glycidyl methacrylate,trimethoxysilyl propyl methacrylate, allyl methacrylate, hydroxyethylmethacrylate, hydroxypropyl methacrylate, dialkylaminoalkylmethacrylates, and fluoroalkyl (meth)acrylates, methacrylic acid,acrylic acid, fumaric acid and esters, itaconic acid (and esters),maleic anhydride, styrene, α-methylstyrene, halogenated alkenes, forexample, vinyl halides, such as vinyl chlorides and vinyl fluorides, andfluorinated alkenes, for example perfluoroalkenes, acrylonitrile,methacrylonitrile, ethylene, propylene, allyl amine, vinylidene halides,butadienes, acrylamide, such as N-isopropylacrylamide, methacrylamide,epoxy compounds, for example glycidoxypropyltrimethoxysilane, glycidol,styrene oxide, butadiene monoxide, ethyleneglycol diglycidylether,glycidyl methacrylate, bisphenol A diglycidylether (and its oligomers),vinylcyclohexene oxide, conducting polymers such as pyrrole andthiophene and their derivatives, and phosphorus-containing compounds,for example dimethylallylphosphonate. Suitable inorganic coating-formingmaterials include metals and metal oxides, including colloidal metals.Organometallic compounds may also be suitable coating-forming materials,including metal alkoxides such as titanates, tin alkoxides, zirconatesand alkoxides of germanium and erbium. However, the present inventorshave found that the present invention has particular utility inproviding substrates with silica- or siloxane-based coatings usingcoating-forming compositions comprising silicon-containing materials.Suitable silicon-containing materials for use in the method of thepresent invention may be selected from the group of silanes (forexample, silane, alkylhalosilanes, alkoxysilanes) and linear (forexample, polydimethylsiloxane) and cyclic siloxanes, for example,octamethylcyclotetrasiloxane, including organo-functional linear andcyclic siloxanes, for example, Si—H containing, halo-functional, andhaloalkyl-functional linear and cyclic siloxanes, e.g.tetramethylcyclotetrasiloxane andtri(nonofluorobutyl)trimethylcyclotrisiloxane. A mixture of differentsilicon-containing materials may be used, for example to tailor thephysical properties of the substrate coating for a specified need e.g.thermal properties, optical properties, such as refractive index, andviscoelastic properties.

[0013] In addition, under oxidizing conditions the present method may beused to form an oxygen containing coating on the substrate. For example,silica-based coatings can be formed on the substrate surface fromatomized silicon-containing coating-forming materials. Under reducingconditions, the present method may be used to form oxygen free coatings,for example, silicon carbide based coatings may be formed from atomizedsilicon containing coating forming materials.

[0014] Plasma generating conditions containing gases other than oxygenmay also be employed, for example noble gases, air, hydrogen, nitrogenand ammonia. In a nitrogen containing atmosphere nitrogen can bind tothe substrate surface, and in an atmosphere containing both nitrogen andoxygen, nitrates can bind to and/or form on the substrate surface. Suchgases may also be used to pre-treat the substrate surface prior toexposure to the coating forming substance. For example oxygen containingplasma treatment of the substrate may provide improved adhesion with theapplied coating. The oxygen containing plasma being generated byintroducing oxygen containing materials to the plasma such as oxygen gasor water. Furthermore, the coating formed on the substrate may be posttreated in a range of plasma conditions. For example, siloxane derivedcoatings may be further oxidized by oxygen containing plasma treatment.The oxygen containing plasma being generated by introducing oxygencontaining materials to the plasma such as oxygen gas or water.

[0015] An advantage of the present invention over the prior art is thatboth liquid and solid atomized coating-forming materials may be used toform substrate coatings, due to the method of the present inventiontaking place under conditions of atmospheric pressure. Furthermore thecoating-forming materials can be introduced into the plasma discharge orresulting stream in the absence of a carrier gas, i.e. they can beintroduced directly by, for example, direct injection, whereby thecoating forming materials are injected directly into the plasma.

[0016] As mentioned above, the present inventors have found particularutility of the present invention for forming silica- and siloxane-basedcoatings on substrates using silicon-containing materials. Underoxidizing conditions, e.g. an oxygen containing atmosphere, silica-basedcoatings can be formed on the substrate surface from atomizedsilicon-containing materials, whereas under non-oxidizing conditions asiloxane polymer, e.g. a linear, branched or resinous siloxane polymer,can be formed on the substrate surface from atomization of asilicon-containing monomer. A siloxane-organic copolymer can be formedon the substrate surface by use of a mixture of organic andsilicon-containing monomers. Furthermore, a silica-based coating may beformed on a substrate surface, which may in turn be coated by a furthermaterial, for example an organic or siloxane polymer. For example, whena siloxane is mixed with an organic polymer and a substrate formed fromsaid mixture, the siloxane will migrate to the surface of the organicpolymeric body of the substrate, due to the difference in surface energybetween organic polymers and siloxanes. If this substrate is thensubjected to atmospheric pressure plasma treatment, the siloxane on thesurface of the substrate is oxidized to form a silica-based coating.This silica-based coating may then be subjected to treatment accordingto the present invention, by further subjecting it to atmosphericpressure plasma treatment in the presence of atomized silicon-containingmonomers, to form a siloxane coating thereon. However, the presentinvention is also useful for forming an organic coating on a substrate,for example a polyacrylic acid or perfluoro-organic coating.

[0017] The substrate to be coated may comprise any material, for examplemetal, ceramic, plastics, siloxane, woven or non-woven fibers, naturalfibers, synthetic fibers cellulosic material and powder. However, thesize of the substrate is limited by the dimensions of the volume withinwhich the atmospheric pressure plasma discharge is generated, i.e. thedistance between the electrodes of the means for generating the plasma.For typical plasma generating apparatus, the plasma is generated withina gap of from 5 to 50 mm, for example 12 to 25 mm. Thus, the presentinvention has particular utility for coating films, fibers and powders.

[0018] Substrates coated by the method of the present invention may havevarious utilities. For example, a silica-based coating, generated in anoxidizing atmosphere, may enhance the barrier and/or diffusionproperties of the substrate, and may enhance the ability of additionalmaterials to adhere to the substrate surface; a halo-functional organicor siloxane coating (e.g. perfluoroalkenes) may increase hydrophobicity,oleophobicity, fuel and soil resistance, and/or the release propertiesof the substrate; a polydimethylsiloxane coating may enhance waterresistance and release properties of the substrate, and may enhance thesoftness of fabrics to touch; a polyacrylic acid polymeric coating maybe used as an adhesive layer to promote adhesion to substrate surface oras part of laminated structure; the inclusion of colloidal metal speciesin the coatings may provide surface conductivity to the substrate, orenhance its optical properties. Polythiophene and polypyrrole giveelectrically conductive polymeric coatings which may also providecorrosion resistance on metallic substrates.

[0019] One major problem that tends to occur when coating substratesusing a process involving plasma treatment is that the chemicalproperties of the material used to form the coating may be lost. It istherefore a major advantage of the present invention that the chemicalproperties of the coating forming material are substantially retained inthe coating formed. For example, in the case where acrylic acid is usedas the coating forming material, the carboxylic acid functionality issubstantially maintained in the coating formed.

[0020] The present invention also provides a method of producing asubstrate having a multi-layered coating by the above-describedprocesses. In this case a layer of the coating is applied upon eachrepeat pass of the substrate through the atmospheric plasma glowdischarge. Preferably in such a case the substrate may be coated on acontinuous basis by being transported through an atmospheric plasma glowdischarge by way of a reel to reel process in which the substratetravels from a first reel, through the glow discharge and on to a secondreel at a constant speed to ensure that all the substrate has apredetermined residence time within the glow discharge. Each substratemay be subjected to one or more passes through the glow dischargewhereby the first or supply reel in the first pass becomes the substratecollecting reel in the second pass and the substrate collecting reel ofthe first pass in turn is the supply reel in the second pass, the tworeels changing over at the end of each pass. Alternatively the substratemay be passed through a series of atmospheric glow discharge chambers.

[0021] Preferred uses of the coatings of the substrates coated inaccordance with the present invention include lamination adhesives,oxygen and/or moisture barrier for example for food packagingapplications and as a component in or on organic light emitting diodedevices in, for example, flat panel displays.

[0022] The present invention will now be illustrated in detail withreference to the accompanying drawing, in which FIG. 1 shows anembodiment of apparatus according to the present invention.

[0023] The apparatus according to the present invention shown in FIG. 1comprises means for generating an atmospheric pressure plasma discharge(generally designated 10), and an atomizer (generally designated 12)connected to a syringe pump 14 for supplying a coating forming materialto the atomizer 12. The means for generating the discharge 10 includes ahigh voltage 15 kHz ac power supply 20, supplied across two aluminumelectrodes 22 and 24 spaced 12 mm apart, with the lower live electrode22 shielded by a glass dielectric plate 26. The atomizer 12 includes aSono-tek 8700-120 ultrasonic nozzle 30 (Sono-tek Corporation, Milton,N.Y. 12547, USA), and is connected to a Sono-tek 06-05108 broadbandultrasonic generator 32. The atomizer 12 is seated within the earthelectrode 24 on an O-ring 34. The substrate 40 to be coated is placed onthe glass dielectric plate 26 between the electrodes 22 and 24.

[0024] The apparatus described hereinabove with reference to FIG. 1 wasused for all the procedures described hereinafter.

EXAMPLES Example 1

[0025] A piece of polyethylene film substrate was ultrasonically washedin a 1:1 mixture of isopropyl alcohol and cyclohexane and was placed onthe glass plate. After evacuation of residual gas, the plasma dischargegas was introduced at a flow rate of 1900 sccm and a pressure of1.02×10⁵ Nm⁻². Two discharge gasses were used, helium and a 99%helium/1% oxygen mixture. After 10 minutes of purging, the syringe pump14 was switched on and the coating-forming material was allowed to flowat a rate of 3×10⁻⁵ mls⁻¹. Two coating-forming materials were used,octamethylcyclotetra-siloxane (hereinafter referred to as “D₄”) andtetramethylcyclotetrasiloxane (hereinafter referred to as “D₄H”). Whenthe coating-forming material reached the ultrasonic nozzle, theultrasonic generator was switched on (2.5 W) to initiate atomization ofthe coating-forming material, and the atmospheric pressure plasmadischarge was ignited by applying 1.5 kV across the electrodes.Deposition of the coating-forming material was allowed to proceed for 10minutes, following which the substrate was removed and placed undervacuum for 20 minutes to remove any labile material.

[0026] The results of the above procedure are shown in Table 1 below.X-ray photoelectron spectroscopic analysis (Kratos ES300) was used toperform elemental analysis of the substrate surface, and aspectrophotometer (Aquila Instruments nkd-6000) was used to determinefilm thickness. Contact angle measurements were made using video captureapparatus (AST Products VCA2500XE) using sessile 2 μl droplets ofdeionised water.

[0027] Gas permeation measurements of the substrate surface were alsotaken using a mass spectrometer, and the results are shown in Table 2.The Barrier Improvement Factor is calculated as [coated substrate gaspermeation]/[reference sample gas permeation]. TABLE 1 Depo- Coatingsition thick- XPS analysis Contact rate ness Sample % C % O % Si %SiO_(x) Angle (°) (nms⁻¹⁾ (nm) D₄ theory 50 25 25 0 — — — D₄ 100% 43.329.3 25.8 107.8* 28 279 He D₄ 1% 25.5 48.5 26.0 74.4 56.4 29 286 O₂ D₄H33.3 33.3 33.3 0 — — — theory D₄H 32.5 39.1 28.4 102.3 82 100% He D₄H 1%9.2 61.4 29.5 81.5 wets 244 O₂

[0028] TABLE 2 Sample Barrier Improvement Factor Clean polyethylene 1.0(by definition) D₄, 100% He 0.9 D₄, 1% O₂ 6.8 D₄H, 100% He 0.9 D₄H,.1%O₂ 4.5

[0029] ATR-FTIR studies of the substrate surfaces showed thatring-opening polymerization of the D₄ and D₄H coating-forming materialshad occurred to form a polysiloxane on the substrate surface. Inparticular, the ATR-FTIR studies on the latter showed that thepolysiloxane coating retained much of the D₄H Si—H functionality.

[0030] NMR studies of a coating prepared as described above on a glasssurface showed that the polysiloxane formed on the substrate surface bypolymerization of the D₄ and D₄H coating-forming materials compriseddivalent (CH₃)₂SiO2/2 units and trivalent CH₃SiO₃/2 units, i.e. thepolysiloxane is resinous.

Example 2

[0031] The method of Example 1 above was repeated using a glasssubstrate and acrylic acid as the coating-forming material, and heliumalone as the discharge gas. The coating was removed from the substrateprior to analysis.

[0032] FTIR and solid state NMR analysis of the coating confirmed thatthe acrylic acid had polymerized to form polyacrylic acid. Both FTIR andNMR data showed consumption of the unsaturated C═C bond.

Example 3

[0033] The method of Example 2 was repeated, but using nylon andpolyethylene substrates.

[0034] An FTIR analysis comparison of the coating with commerciallyavailable polyacrylic acid confirmed that the acrylic acidcoating-forming material had polymerized to form a polyacrylic acidcoating on the substrate surfaces.

[0035] X-ray photoelectron spectroscopic analysis, film thicknessanalysis, and contact angle measurements were performed per Example 1above. The results are shown in Table 3 below. TABLE 3 ContactDeposition XPS analysis Angle rate % C % O % CO₂H (°) (nms⁻¹) Theory60.0 40.0 33.3 — — Commercial polyacrylic 63.3 36.7 29.9 wets — acidExample 3 coating 62.6 37.4 26.4 wets 231 ± 95

[0036] Gas transport through the coated polyethylene film was determinedby mass spectrometry, and the barrier improvement factor calculated perExample 1 above over an untreated polyethylene substrate andcommercially available polyacrylic acid. The results are shown in Table4 below. TABLE 4 Sample Barrier Improvement Factor Untreated substrate1.0 (by definition) Commercial polyacrylic acid 1.1 ± 0.1 Example 3coating 7.2 ± 0.9

[0037] A lap shear test was performed on the coated nylon substrates asfollows. Two opposing faces of coated nylon substrates were overlappedto create a joint covering 1 cm², and the substrates were cured under a2 kg weight at 70° C. for 60 minutes. The adhesive strength of eachjoint was then determined by pulling the substrates apart at a rate of 5mm per minute using a tensilometer (Instron), and recording the maximumload reached prior to failure. The coated substrates withstood a maximumload of 74±11 Ncm ⁻² prior to failure. Comparison joints made fromuncoated nylon displayed no adhesive properties.

Example 4

[0038] The method of Example 2 was repeated, using a glass substrate and1H,1H,2H-perfluoro-1-octene (CF₃(CF₂)₅CH═CH₂) as the coating-formingmaterial.

[0039] X-ray photoelectron spectroscopic analysis, FTIR analysis andcontact angle measurements (with water and decane) were performed perExample 1 above, and results are shown in Table 5 below. The XPS andFTIR analysis showed that the glass substrate coating was rich in CF₂and CF₃ and the contact angles for water and decane were determined asper example 1. TABLE 5 XPS analysis Contact Angle (water) Contact Angle% C % F % O (°) (decane) (°) Theory 38.1 61.9 — — — Example 4 38.0 60.02.1 118.9 ± 3.0 61.1 ± 2.2 coating

[0040] The contact angle measurement results show that the glasssubstrate has been rendered substantially

[0041] 1. A method for forming a coating on a substrate, the methodcomprising introducing a material selected from the group consisting of:

[0042] (i) an atomized liquid and

[0043] (ii) a solid coating-forming material into an atmosphere selectedfrom:

[0044] (a) an atmospheric pressure plasma discharge and

[0045] (b) an ionized gas stream resulting therefrom,

[0046] and exposing the substrate to the atomized coating-formingmaterial under conditions of atmospheric pressure.

[0047] 2. A method according to claim 1 wherein the coating-formingmaterial is introduced by direct injection.

[0048] 3. A method according to claim 1 wherein the coating-formingmaterial is a silicon-containing material.

[0049] 4. A method according to claim 3 wherein the coating-formingmaterial is selected from a dimethylsiloxane, and a siloxane havingsilicon-hydrogen bonds.

[0050] 5. A method according to claim 1 wherein the plasma is generatedin an oxygen containing atmosphere.

[0051] 6. A method according to claim 1 wherein the coating-formingmaterial is selected from a group consisting of:

[0052] (i) an organic material, and

[0053] (ii) an organometallic material.

[0054] 7. A method according to claim 6 wherein the coating-formingmaterial is selected from the group consisting of:

[0055] (i) an acrylic acid and

[0056] (ii) a perfluoroalkene.

[0057] 8. A method according to claim 1 wherein the substrate isselected from the group consisting of:

[0058] (i) a metal,

[0059] (ii) ceramic,

[0060] (iii) plastics,

[0061] (iv) woven fibers,

[0062] (v) non-woven fibers,

[0063] (vi) natural fibers,

[0064] (vii) synthetic fibers,

[0065] (viii) cellulosic material, and

[0066] (ix) powder.

[0067] 9. A method according to claim 1 wherein the coating increases atleast one of the properties selected from the group consisting of:

[0068] (i) adhesive properties,

[0069] (ii) release properties,

[0070] (iii) gas barrier properties,

[0071] (iv) moisture barrier properties,

[0072] (v) electrical properties,

[0073] (vi) thermal conductivity properties,

[0074] (vii) optical properties,

[0075] (viii) dielectric properties,

[0076] (ix) hydrophilic properties,

[0077] (x) hydrophobic, properties and

[0078] (xi) oleophobic properties of the substrate.

[0079] 10. A method of producing a substrate having a multi-layeredcoating according to claim 1 whereby the coating is applied byrepeatedly passing said substrate through the atmospheric plasma glowdischarge.

[0080] 11. A method of producing a substrate having a multi-layeredcoating according to claim 1 by passing said substrate through a seriesof atmospheric glow discharge chambers.

[0081] 12. A method according to claim 1 wherein the chemical propertiesof the atomized liquid forming material are substantially retained inthe resulting coating formed.

[0082] 13. A method according to claim 1 wherein the chemical propertiesof the atomized solid coating forming material are substantiallyretained in the resulting coating formed.

[0083] 14. A method in accordance with claim 1 wherein the substrate iscoated continuously by use of a reel to reel apparatus.

[0084] 15. A method in accordance with claim 1 wherein the substrate ispre-treated by exposure to plasma prior to the introduction of coatingforming material.

[0085] 16. A method in accordance with claim 14 wherein the plasma isapplied by way of atmospheric pressure glow discharge.

[0086] 17. A method in accordance with claim 15 wherein an oxygencontaining material is added to the plasma.

[0087] 18. A method in accordance with claim 16 wherein the oxygencontaining materials are selected from the group consisting of:

[0088] (i) oxygen gas and

[0089] (ii) water.

[0090] 19. A method in accordance with claim 1 wherein the coatingformed on the substrate is post-treated by exposure to plasma.

[0091] 20. A method in accordance with claim 18 wherein the plasma isapplied by way of atmospheric pressure glow discharge.

[0092] 21 A method in accordance with claim 19 wherein an oxygencontaining material is added to the plasma.

[0093] 22. A method in accordance with claim 20 wherein the oxygencontaining materials are selected from the group of oxygen gas andwater.

[0094] 23. Apparatus for forming a coating on a substrate underconditions of atmospheric pressure, which apparatus comprises device forgenerating an atmospheric pressure plasma glow discharge within which,in use, the substrate is placed, an atomizer for providing an atomizedcoating-forming material within the plasma discharge, and a device forsupplying said coating forming material to the atomizer.

[0095] 24. Apparatus in accordance with claim 22 wherein the atomizer isan ultrasonic nozzle.

[0096] 25. Apparatus in accordance with claim 22 wherein the substrateis fixed to a reel to reel apparatus to enable a continuous coating ofthe substrate.

[0097] 26. A method for co-polymerizing a liquid coating—forming monomermaterial under conditions of atmospheric pressure, which methodcomprises atomizing the monomer material, and exposing the atomizedmonomer material to an atmospheric pressure plasma discharge.

[0098] 27. A method for co-polymerizing a solid coating—forming monomermaterial under conditions of atmospheric pressure, which methodcomprises atomizing the monomer material, and exposing the atomizedmonomer material to an atmospheric pressure plasma discharge.

1. A method for forming a coating on a substrate, which method comprisesintroducing an atomised liquid and/or solid coating-forming materialinto an atmospheric pressure plasma discharge and/or an ionised gasstream resulting therefrom, and exposing the substrate to the atomisedcoating-forming material.
 2. A method according to claim 1 wherein thecoating-forming material is introduced by direct injection.
 3. A methodaccording to claim 1 or 2 wherein the coating-forming material is asilicon-containing material.
 4. A method according to claim 3 whereinthe coating-forming material is selected from a dimethylsiloxane, and asiloxane having silicon-hydrogen bonds.
 5. A method according to anypreceding claim wherein the plasma is generated in an oxygen containingatmosphere.
 6. A method according to claim 1 or 2 wherein thecoating-forming material is an organic or organometallic material.
 7. Amethod according to claim 6 wherein the coating-forming material isselected from acrylic acid and a perfluoroalkene.
 8. A method accordingto any preceding claim wherein the substrate comprises metal, ceramic,plastics, woven or non-woven fibres, natural fibres, synthetic fibres,cellulosic material, and powder.
 9. A method according to any precedingclaim wherein the coating increases the adhesive, release, gas barrier,moisture barrier, electrical and thermal conductivity, optical,dielectric, hydrophilic, hydrophobic, and/or oleophobic properties ofthe substrate.
 10. A method of producing a substrate having amulti-layered coating according to any preceding claim whereby thecoating is applied by repeatedly passing said substrate through theatmospheric plasma glow discharge or by passing said substrate through aseries of atmospheric glow discharge chambers.
 11. A method forpolymerising a polymer forming material, which method comprisesatomising the polymer-forming material, and exposing the atomisedpolymer-forming material to an atmospheric pressure plasma discharge.12. A method according to any one of claims 1 to 4,6 or 7 wherein thechemical properties of the atomised liquid and/or solid coating formingmaterial are substantially retained in the resulting coating formed. 13.A method in accordance with any preceding claim wherein the substrate iscoated continuously by use of a reel to reel apparatus.
 14. A method inaccordance with any preceding claim wherein the substrate is pre-treatedby exposure to plasma prior to the introduction of coating formingmaterial.
 15. A method in accordance with any preceding claim whereinthe coating formed on the substrate is post-treated by exposure toplasma.
 16. A method in accordance with claim 14 or 15 wherein theplasma is applied by way of atmospheric pressure glow discharge.
 17. Amethod in accordance with claim 16 wherein an oxygen containing materialis added to the plasma.
 18. A method in accordance with claim 17 whereinthe oxygen containing materials are selected from the group of oxygengas and water.
 19. Apparatus for forming a coating on a substrate, whichapparatus comprises means for generating an atmospheric pressure plasmaglow discharge within which, in use, the substrate is placed, anatomiser for providing an atomised coating-forming material within theplasma discharge, and means for supplying a coating forming material tothe atomiser.
 20. Apparatus in accordance with claim 19 wherein theatomiser is an ultrasonic nozzle.
 21. Apparatus in accordance with claim19 or 20 wherein the substrate is fixed to a reel to reel apparatus toenable a continuous coating of the substrate.
 22. A coated substrateprepared in accordance with the method of any one of claims 1 to
 18. 23.A coated substrate in accordance with claim 22 wherein the chemicalproperties of the atomised liquid and/or solid coating forming materialare retained in the resulting coating.
 24. Use of a coated substrateformed in accordance with the method of any one of claims 1 to 18 as alamination adhesive, an oxygen and/or moisture barrier or in organiclight emitting diode devices.